A spin coating method is commonly used in forming a coating film, for example, a resist film, on a substrate. In this method, a resist solution as a coating solution is supplied to a central portion of a surface of the substrate supported in a spin chuck and rotated, and the resist solution is spread to a peripheral portion of the substrate by a centrifugal force, and thereafter, the substrate is continuously rotated to dry a liquid film of the surface of the substrate to form the resist film. A completed film thickness (target film thickness) of the resist film is adjusted by a revolution per minute (RPM) of the substrate or viscosity of the resist solution.
In a factory, there is a request for forming resist films having various film thicknesses in each process using the same resist solution, namely, the same type of resist solution and solvent having the same viscosity. However, when a film is formed on a surface of a substrate through spin coating, if an RPM of the substrate is too high, there is a possibility that a surface of the film is damaged by an air current formed on the substrate. On the other hand, if the RPM is too low, the time required for drying is lengthened.
For this reason, the usable range of the RPM of the substrate is limited, and thus, an adjustment range of a film thickness of the resist film formed using the same resist solution is limited. Therefore, in order to form a resist film having a film thickness exceeding the adjustment range, it is required to prepare resist solutions having different viscosities. In this case, a coating solution line may be prepared for each viscosity of resist solution, or in case of using a common coating solution line, a tank of resist solution is required to be exchanged, causing a device to be increased in size or complexity of an operation.
One of the related arts discloses a technique of supplying a solvent gas to a region of a substrate in which a thick film is formed and supplying a dry gas to a region of the substrate in which a thin film is formed to make a film thicknesses uniform. However, the related art does not disclose a technique of adjusting an average film thickness of a formed coating film.